The goals of this project are to analyze the individual contribution and the cellular interactions of at least two bone cell types during hormonal stimulation of bone. To facilitate such studies, we plan to continue our efforts to obtain highly purified populations of osteoclast-like and osteoblast-like cells which will be used as model systems. Physical separation of cells on density gradients, selective cytotoxicity with drugs, selective cell growth in various hormones and selective cell separation using antibodies to cell surface proteins will be used to further fractionate bone cell populations obtained by sequential digestion of mouse calvaria. Cell fractions deemed highly enriched for OC and OB biochemical marker activities will be used to further study the basal metabolism, pharmacological characteristics and the molecular intermediates involved in hormone action on each cell type. We have shown that OC and OB cells differ in their susceptibility to glucocorticoids, in their PTH coupled adenylated cyclase response to trifluoperazine, in their metabolism of PTH receptors and in their biochemical responses to bone active hormones. Further characterization of these two major bone cell types may provide information on their individual responses to environmental agents. In addition, by studying the changes induced in each cell type in a defined situation we may be able to reconstruct the tissue response and the modulations operating on this response under various physiological conditions. Since osteoclast induced bone resorption is normally balanced by osteoblast dependent bone formation in the healthy adult, and inequities in these processes result in metabolic bone disease, these studies may serve to illustrate possible origins as well as palliative measures against certain metabolic bone diseases.